The aim of this research was to determine the accumulation of aerial biomass and the amount and quality of essential oils that can be obtained from thyme (Thymus vulgaris L.) under organic and mineral fertilization based on days to harvest. The experiment was conducted in a greenhouse during the 2007 spring-summer season with a commercial cultivar of thyme. A randomized complete block experimental design with five replications and a factorial arrangement was used. There were three harvests at 60, 90 and 120 days after transplantation. The organic fertilization was with applications of humic acid in the irrigation and by adding a liquid fertilizer combined with biosynthetic amino acids. Steiner solution at 75% concentration was used for the inorganic fertilization as mineral treatment. Plant height, fresh and dry biomass of the plant, and main stem diameter were evaluated. Essential oils were extracted from 50 g of fresh plant material using steam distillation of water. The concentration (μg/ml) of thymol and carvacrol was determined. Quantitative and qualitative comparisons were carried out by thin layer chromatography (TLC) and gas chromatography-mass spectrometry (GC-MS), respectively. The results show that inorganic fertilization increased plant height (PH) by 36.8%, fresh shoot biomass (FSB) by 72.19%, fresh root biomass (FRB) by 59.27%, stem diameter (SD) by 12.15%, and dry shoot biomass (DSB) and dry root biomass (DRB) by 69.85% and 68.15%, respectively. Days to harvest (DH) influenced positively (p≤0.05) the evaluated morphological characters but they did not show differences in the total yield of essential oil. Mineral fertilizing increased the concentration (μg/ml) of thymol (46%) and carvacrol (38.4%) at 90 DH.